Piezofluorochromic properties of AIE-active 9,10-bis(N-alkylpheno-thiazin- 3-yl-vinyl-2)anthracenes with different length of alkyl chains

Article abstract of DOI:10.1016/j.dyepig.2013.10.020

9,10-Bis(N-alkylphenothiazin-3-yl-vinyl-2)anthracenes (PT-Cn) with different carbon numbers (n) of alkyl chains (n = 2, 3, 5, 6, 7, 9, 12, 18) are prepared to further understand the effect of alkyl lengths on the solid-state fluorescence and piezochromic luminescence of alkyl-containing 9,10-bis(arylvinyl)anthracenes. The results show that the fluorescence emissions of both pressed and annealed PT-Cn are gradually blue-shifted, but the blue-shifted amplitudes of annealed states are more remarkable with the increase of alkyl length, leading to that longer alkyl-containing PT-Cn show larger piezofluorochromism (PFC) spectral shifts. Powder wide-angle X-ray diffraction and differential scanning calorimetry experiments reveal that the transformation between crystalline and amorphous states under various external stimuli is responsible for the PFC and restoration behaviors. This work demonstrates once again that combining the simple alternation of molecular chemical structure and the physical change of aggregate morphology under external stimuli could tune the solid-state optical properties of some organic fluorophores.

Full text of DOI:10.1016/j.dyepig.2013.10.020

Dyes and Pigments 102 (2014) 29e34
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Piezofluorochromic properties of AIE-active 9,10-bis(N-alkylpheno-
thiazin-3-yl-vinyl-2)anthracenes with different length of alkyl chains
Meng Zheng, Mingxiao Sun, Yiping Li, Jianfeng Wang, Lingyu Bu, Shanfeng Xue,
Wenjun Yang*
Key Laboratory of Rubber-Plastics of Ministry of Education/Shandong Province (QUST), School of Polymer Science & Engineering, Qingdao University of
Science & Technology, 53-Zhengzhou Road, Qingdao 266042, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 5 August 2013
Received in revised form
9,10-Bis(N-alkylphenothiazin-3-yl-vinyl-2)anthracenes (PT-Cn) with different carbon numbers (n) of
alkyl chains (n ¼ 2, 3, 5, 6, 7, 9, 12, 18) are prepared to further understand the effect of alkyl lengths on the
solid-state fluorescence and piezochromic luminescence of alkyl-containing 9,10-bis(arylvinyl)anthra-
cenes. The results show that the fluorescence emissions of both pressed and annealed PT-Cn are grad-
ually blue-shifted, but the blue-shifted amplitudes of annealed states are more remarkable with the
increase of alkyl length, leading to that longer alkyl-containing PT-Cn show larger piezofluorochromism
1
October 2013
Accepted 9 October 2013
Available online 29 October 2013
(
PFC) spectral shifts. Powder wide-angle X-ray diffraction and differential scanning calorimetry experi-
Keywords:
ments reveal that the transformation between crystalline and amorphous states under various external
stimuli is responsible for the PFC and restoration behaviors. This work demonstrates once again that
combining the simple alternation of molecular chemical structure and the physical change of aggregate
morphology under external stimuli could tune the solid-state optical properties of some organic
fluorophores.
9,10-Bis(N-alkylphenothiazin-3-yl-vinyl-2)
anthracenes
Piezofluorochromism
Aggregation-induced emission
N-alkyl length-dependency
WittigeHorner reaction
End group effect
Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction
containing conjugated molecules are alkyl length-dependent, such
as 9,10-bis(p-alkoxystyryl)anthracences only with sufficient long
Conjugated organic molecules exhibiting strong solid-state
fluorescence are promising optical and optoelectronic materials,
and tuning and switching the solid-state luminescence by external
mechanical stimuli (such as grinding, pressing, shearing, defor-
mation, etc. named mechano- or piezo-fluorochromism (PFC)),
instead of the chemical alteration of molecular structures not only
have potential applications in chemo- and mechano-sensors, data
storage, security inks and optoelectronic devices but also profit the
understanding of solid-state photophysical properties [1e8].
Recent studies have demonstrated that conjugated molecules
with strongly twisted skeleton conformations not only show
aggregation-induced/crystallization-enhanced emission but also
are mostly promising candidates for PFC materials [8e26]. In this
context, 9,10-bis(arylvinyl)anthracene derivatives have been the
mainstay of PFC materials reported to date [17,23e32]. Interest-
ingly, recent several reports show that PFC behaviors of some alkyl-
alkyl chains (n ꢀ 10, n represents carbon number of alkyl chains)
are effective PFC materials [29], and 9,10-bis[(N-alkylcarbazol-3-yl)
vinyl]- and 9,10-bis[(9,9-dialkyl-fluorene-2-yl)vinyl]anthracenes
exhibit different alkyl length-dependent PFC behaviors [24,28], etc.
These results not only underline the complexity of the structuree
property relationship of PFC materials but also indicate the signif-
icant effect of the nature of end-aryl and substituents at the aryl
rings on the solid-state fluorescence and piezochromic lumines-
cence. 9,10-bis(N-alkylphenothiazin-3-yl-vinyl-2)anthracenes are
also alkyl-containing 9,10-bis(arylvinyl)anthracene derivatives, and
one of them, 9,10-bis(N-hexylphenothiazin-3-yl-vinyl-2)anthra-
cene has been found to show remarkable PFC behavior [33]. To
further understand the effect of alkyl chains on the solid-state
fluorescence and piezochromic luminescence, in the current
work, we have prepared a series of 9,10-bis(N-alkylphenothiazin-3-
yl-vinyl-2)anthracenes (PT-Cn) with different length of alkyl chains
(
n ¼ 2, 3, 5, 6, 7, 9, 12, 18. Scheme 1) and their fluorescence prop-
erties are investigated. We now report that the solid-state fluo-
rescence emissions and PFC spectral shifts of PT-Cn are indeed
related to the length of alkyl chains.
*
Corresponding author. Tel.: þ86 532 84023670; fax: þ86 532 84023977.
E-mail address: ywjph2004@qust.edu.cn (W. Yang).
0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2013.10.020

30
M. Zheng et al. / Dyes and Pigments 102 (2014) 29e34
C H
CnH2n+1
N
n
2n+1
H
N
N
POCl /DMF
NaOH/DMS O
3
C H2n+1Br
n
S
CHO
2n+1
S
S
B
A
(
E tO) OP
2
C H
n
S
N
C
PO(OE t)2
N
S
t-BuOK/THF
H2n+1Cn
PT-Cn (n = 2, 3, 5, 6, 7, 9, 12, 18)
Scheme 1. Synthetic route and structure of PT-Cn.
2
. Experimental section
2.4. Synthesis
2
.1. Reagents and solvents
2.4.1. 9,10-Bis(2-(10-hexylphenothiazin-3-yl)vinyl)anthracene
PT-C7)
9,10-Bis(di-ethylphosphorylmethyl)anthracene (0.10 g, 0.21
(
All the starting chemicals were purchased from Aldrich Chem-
ical Co. Other solvents and reagents were analytical grade and used
as received, unless otherwise stated. 9,10-bis(diethylphosphor-
ylmethyl)anthracene was from previous work [34]. THF was
distilled over metallic sodium and DMF over calcium hydride
before use.
mmol) and 10-heptylphenothiazine-3-carbaldehyde (0.150 g,
0.46 mmol) was dissolved in anhydrous THF (20 mL). Potassium
tert-butoxide (0.19 g, 1.67 mmol) was added and the suspension
was stirred for 3 h at room temperature. Methanol was added into
the mixture and a yellow-green solid was collected by filtration.
The crude product was purified by silica gel column chromatog-
raphy (petroleum ether/methylene chloride
yellowish-green solid with a yield of 75% (0.19 g) was obtained. H
NMR (500 MHz, CDCl ): 8.37 (q, 4H), 7.80 (s, 1H), 7.77 (s, 1H),
.40e7.50 (m, 8H), 7.15e7.28 (m, 4H), 6.89e7.05 (m, 6H), 6.82 (s,
¼
4:1, v/v). A
2
.2. Measurement
1
3
d
1H and 13C NMR spectra were recorded on a Bruker-AC500
7
1
0
3
spectrometer with CDCl as solvent and teramethylsilane (TMS)
H), 6.78 (s, 1H), 3.90 (t, 4H), 1.86 (qui, 4H), 1.29e1.56 (m, 16H),
as the internal standard. Elemental analysis was performed on
PerkineElmer 2400. UVevis absorption spectra were recorded on a
Hitachi U-4100 spectrophotometer. Fluorescence measurements
were carried out with Hitachi F-4600 spectrophotometer. The peak
wavelength of the lowest energy absorption band was used as the
excitation wavelength for the PL measurement. The fluorescence
1
3
.89 ppm (t, 6H). C NMR (125 MHz, CDCl
32.68, 131.91, 129.63, 127.49, 127.30, 126.47, 125.94, 125.38, 125.17,
24.99, 124.36, 123.42, 122.48, 115.40, 47.54, 31.92, 29.69, 29.36,
6.93, 22.62, 14.14 ppm. Anal. Calcd for C56 (%): C, 81.91; H,
3
): d 145.01, 136.19,
1
1
2
6
56 2 2
H N S
.87; N, 3.41; S, 7.81. Found: C, 81.86; H, 6.91; N, 3.39; S, 7.85.
Other 9,10-bis(2-(10-alkylphenothiazin-3-yl)vinyl)anthracenes
quantum yield (F) was determined at room temperature by the
were synthesized as described for PT-C7 except that different 10-
alkylphenothiazine-3-carbaldehydes were used. After purification,
dilution method using fluorescein in water (pH ¼ 11) as the refer-
ence. Powder wide-angle X-ray diffraction (PXD) experiments were
performed on a Powder X-ray Diffractometry (INCA Energy, Oxford
Instruments) operating at 3 kW. Differential scanning calorimetry
1
they were characterized only by H NMR because of their similar
1
and simple structure. The H NMR data were as follow:
(
DSC) curves were determined on a Netzsch DSC 204F1 at a heating
2
.4.2. 9,10-Bis(2-(10-ethylphenothiazin-3-yl)vinyl)anthracene (PT-C2)
ꢁ
rate of 10 C/min.
1
3
H NMR (500 MHz, CDCl ) d 8.36 (q, 4H), 7.80 (s, 1H), 7.76 (s, 1H),
7.40e7.49 (m, 8H), 7.16e7.27 (m, 4H), 6.89e7.03 (m, 6H), 6.82 (s,
2.3. Piezofluorochromic and stimulus-recovering experiments
1H), 6.78 (s, 1H), 3.86 (t, 4H), 0.98 ppm (t, 6H).
Pressing experiment: A quantity of PT-Cn and KBr powder was
2.4.3. 9,10-Bis(2-(10-propylphenothiazin-3-yl)vinyl)anthracene
simply mixed in a mortar and then pressed with IR pellet press
under the pressure of 1500 psi for 1 min at room temperature.
(PT-C3)
1H NMR (500 MHz, CDCl
) d 8.37 (q, 4H), 7.81 (s, 1H), 7.75 (s, 1H),
3
Annealing experiment: The pressed sample (or molten solid) was
7.40e7.49 (m, 8H), 7.16e7.26 (m, 4H), 6.89e7.02 (m, 6H), 6.82 (s,
1H), 6.78 (s, 1H), 3.85 (t, 4H), 1.86 (q, 4H), 0.90 ppm (t, 6H).
ꢁ
put into an oven whose temperature was 40 C over T
c
(cold-
crystallization temperature of each compound) for 2 min. Solvent-
fuming experiment: The pressed sample was put above the
dichloromethane level and exposed to the vapor for 1 min at room
temperature. Grinding experiment: pristine solids were put on a
glass plate and ground with a metal spatula at room temperature.
2.4.4. 9,10-Bis(2-(10-pentylphenothiazin-3-yl)vinyl)anthracene
(PT-C5)
1H NMR (500 MHz, CDCl
)
d
8.37 (q, 4H), 7.77 (s, 1H), 7.75 (s, 1H),
3
7.45e7.47 (m, 8H), 7.16e7.26 (m, 4H), 6.89e7.02 (m, 6H), 6.82

M. Zheng et al. / Dyes and Pigments 102 (2014) 29e34
31
ꢃ5
Fig. 1. Emission (PL) spectra of PT-Cn at 1.0 ꢂ 10 M in watereTHF mixtures; the insets are the fluorescence images with water contents of 0% and 90% under illumination with a
65 nm UV lamp.
3
(
0
s, 1H), 6.78 (s, 1H), 3.90 (t, 4H), 1.86 (q, 4H), 1.29e1.56 (m, 8H),
.92 ppm (t, 6H).
contrast to the faint fluorescence of PT-Cn in THF, the aqueous
dispersions of PT-Cn in THFewater mixtures at high water content
exhibit strong fluorescence. Since water is the non-solvent for PT-
Cn, the molecules of PT-Cn must have aggregated in THFewater
mixtures with high water content. Therefore, PT-Cn homologs are
strongly AIE-active. In addition, the aqueous dispersions of PT-Cn
prepared by us emit bright orange fluorescence. Fig. 2 shows the
fluorescence emission spectra of as-prepared (pristine) PT-Cn solids
by evaporating the solvents (petroleum ether/methylene chloride).
Among them, pristine PT-C18 solid exhibits the most blue-shifted
emission, and others are related irregularly to alkyl length.
2
.4.5. 9,10-Bis(2-(10-hexylphenothiazin-3-yl)vinyl)anthracene (PT-
C6)
1H NMR (500 MHz, CDCl
.39e7.49 (m, 8H), 7.14e7.25 (m, 4H), 6.88e7.94 (m, 6H), 6.80 (s,
3
) d 8.34 (q, 4H), 7.80 (s, 1H), 7.76 (s, 1H),
7
1
0
H), 6.77 (s, 1H), 3.89 (t, 4H), 1.84 (q, 4H), 1.29e1.56 (m, 12H),
.89 ppm (t, 6H).
2
.4.6. 9,10-Bis(2-(10-nonylphenothiazin-3-yl)vinyl)anthracene
(
PT-C9)
1H NMR (500 MHz, CDCl
.40e7.50 (m, 8H), 7.15e7.28 (m, 4H), 6.89e7.02 (m, 6H), 6.82 (s,
H), 6.78 (s, 1H), 3.90 (t, 4H), 1.86 (q, 4H), 1.27e1.56 (m, 24H),
.88 ppm (t, 6H).
The PFC and recovery behavior of PT-Cn (mixed with KBr to
minimize the amount of fluorophores) is examined (Fig. 3). When
they are pressed with an IR pellet press (30 s at 1500 psi), the
pressed samples show red to orange colors from PT-C2 to PT-C18.
However, when the pressed samples are annealed before the
isotropic melt transition or exposed to solvent vapor (fuming above
dichloromethane), the fluorescence colors are changed into
orange-yellow to green ones. Furthermore, when the fumed or
annealed samples are re-pressed, the fluorescence colors are again
changed as the first pressing. This process is reproducible, indi-
cating a reversible PFC behavior. It is noted that PT-Cn with long
alkyl chains exhibit more remarkable fluorescence color changes
between pressed and annealed (or fumed) states.
3
) d 8.36 (q, 4H), 7.80 (s, 1H), 7.77 (s, 1H),
7
1
0
2
.4.7. 9,10-Bis(2-(10-dodecylphenothiazin-3-yl)vinyl)anthracene
(
PT-C12)
1H NMR (500 MHz, CDCl
.40e7.50 (m, 8H), 7.16e7.27 (m, 4H), 6.89e6.95 (m, 6H), 6.82 (s,
3
) d 8.36 (q, 4H), 7.80 (s, 1H), 7.77 (s, 1H),
7
1
0
H), 6.79 (s, 1H), 3.90 (t, 4H), 1.85 (q, 4H), 1.26e1.56 (m, 36H),
.88 ppm (t, 6H).
2
.4.8. 9,10-Bis(2-(10-octadecylphenothiazin-3-yl)vinyl)anthracene
Meanwhile, the emission spectra of above samples under
various stimuli are recorded on a luminescence spectrophotometer
(Fig. 4), and the corresponding peak emission wavelengths (l) are
summarized in Table 1. It is shown that the emission spectra are
very consistent with the corresponding fluorescence colors
(
PT-C18)
1H NMR (500 MHz, CDCl
.40e7.50 (m, 8H), 7.15e7.26 (m, 4H), 6.88e6.95 (m, 6H), 6.82 (s,
3
)
d
8.36 (q, 4H), 7.80 (s, 1H), 7.77 (s, 1H),
7
1
0
H), 6.79 (s, 1H), 3.90 (t, 4H), 1.85 (q, 4H), 1.25e1.49 (m, 60H),
.87 ppm (t, 6H).
observed (Figs. 4 and 3). The
lpressed and
lannealed all decreased with
the increase of alkyl length, and the decrease of
lannealed is more
obvious (Table 1). Although short alkyl (C2, C3, and C5) and middle
3
. Results and discussion
Synthetic route and structure of 9,10-bis(2-(10-octadecylp
henothiazin-3-yl)vinyl)-anthracenes (PT-Cn) was depicted in
Scheme 1. The alkylation of phenothiazine with different n-alkyl
bromides followed by the treatment with POCl
alkyl-3-formylphenothiazines (B) with different length of alkyl
chains [35]. The WittigeHorner reaction of and 9,10-
3
/DMF produced 10-
B
bis(diethylphosphorylmethyl)anthracene (C) afforded the target
compounds PT-Cn in good high yields (75e91%) [35]. The chemical
composition and structure of these products were confirmed by
proton nuclear magnetic resonance spectra and elemental analysis.
PT-Cn homologs are all highly soluble in common organic sol-
vents, such as THF, chloroform, dichloromethane, and toluene. To
understand whether these water-nonsoluble conjugated organic
molecules are aggregation-induced emission (AIE) active, a large
amount of water was added into the organic solution of the com-
pound and the change of fluorescence intensity recorded (Fig. 1). In
Fig. 2. Emission spectra pristine PT-Cn solids.

32
M. Zheng et al. / Dyes and Pigments 102 (2014) 29e34
Table 1
Peak emission wavelengths (l, in nm) of PT-Cn solids under various external stimuli.
PT-Cn
C2
C3
C5
C6
C7
C9
C12
C18
l
l
l
l
pressed
620
577
621
572
43
608
568
614
553
40
607
563
608
560
44
605
554
605
541
51
600
546
604
537
54
599
547
600
546
52
595
537
601
534
58
588
517
593
514
71
annealed
repressed
fumed
a
DlPFC
a
DlPFC
¼
l
pressed
ꢃ
annealed
l .
alkyl (C6, C7, and C9) PT-Cn show similar pressing-induced spectral
shifts (DlPFC annealed), respectively (Table 1), the general
¼
l
pressed
ꢃ
l
trend of DlPFC increases with the length of alkyl chains. Therefore,
PT-Cn homologs are also alkyl chain length-dependent PFC mate-
rials, and alkyl chains have played a functional role in tuning the
PFC behavior. Without doubt, X-ray analysis of single crystals
should give more accurate information. Unfortunately, the single
crystals of long alkyl-containing PT-Cn such as PT-C12 and PT-C18
suitable for X-ray analysis are not obtained, and the origin for this
alkyl chain length-dependent PFC behavior is not clear at present.
To gain an insight into the PFC behavior of PT-Cn solids,
powder wide-angle X-ray diffraction (PWXD) and differential
scanning calorimetry (DSC) experiments are conducted on the
pristine and ground solids. As shown in Fig. 5(a), pristine solids
show sharp and intense reflections, indicative of the well-ordered
microcrystalline structures. In contrast, the ground solids display
Fig. 3. Fluorescence images of PT-Cn mixed with KBr upon external stimuli under a
65 nm UV lamp.
3
Fig. 4. Normalized emission spectra of PT-Cn mixed with KBr upon external stimuli and image of TP-C18 casted on a filter paper and drawn a windmill with a metal spatula.

M. Zheng et al. / Dyes and Pigments 102 (2014) 29e34
33
Fig. 5. Powder X-ray diffraction patterns at room temperature (a) and DSC curves (b) of pristine and ground PT-Cn solids.
Fig. 6. Images of PT-Cn solids after melting and then annealing under illumination of 365 nm UV lamp (left) and normalized emission spectra under quenched melt states (right).
broad and featureless reflections along with a series of over-
lapped peaks reflecting notable amorphous features. Therefore,
grinding has induced the phase transition of PT-Cn solids be-
tween crystalline and amorphous states, which should be
responsible for their PFC behavior. This PFC mechanism could be
confirmed by DSC experiments. Fig. 5(b) shows that no additional
thermal transitions are detected for all pristine solids before the
isotropic melt transition; however, there is clearly one
exothermic transition peak at the lower-temperature region for
respective ground solids. This broad exothermic peak could be
ascribed to the cold-crystallization of amorphized PT-Cn solids
upon heat annealing [24,28].
To further understand experimentally the contribution of
amorphizationecrystallization transition to the PFC behavior of PT-
Cn, PT-Cn solids are melted and then quenched in liquid nitrogen,
which could be considered to afford real amorphous solids. It is
observed that both the just quenched and long-time parked melts
at room temperature show similar fluorescence images and emis-
sion spectra (Fig. 6), which are also similar to those of pressed
samples (vide supra). When the quenched melts are annealed
before respective melt points, the blue-shifted fluorescence colors
are observed, same as above pressed samples upon annealing. This
finding evidences further that the transformation between crys-
talline and amorphous states upon various external stimuli is
responsible for the PFC behavior of PT-Cn.
induced emission homologs exhibit alkyl length-related piezo-
fluorochromic (PFC) behavior whose PFC spectral shifts (DlPFC
)
increase with the extension of alkyl length. PT-Cn homologs
become new alkyl chain length-dependent PFC materials, and a
remarkable DlPFC up to 71 nm for PT-C18 is observed. PFC mecha-
nism that the transformation between crystalline and amorphous
states upon external stimuli is revealed by power X-ray diffraction
and differential scanning calorimetry analysis and further evi-
denced by melt-crystallization experiment. This work demon-
strates once again that subtle manipulation of end groups of 9,10-
divinylanthracene derivatives could endow them with unique and
tunable solid-state optical properties. The revelation of alkyl
length-dependent PFC behavior is a challenging subject and is
underway in our laboratory.
Acknowledgment
We thank the NSF of China (No. 51173092, 51073083, 51303091),
NSF of Shandong Province and Qingdao City (No. ZR2010EM023,
ZR2012EMQ003, 13-1-4-207-jch), and the Doctoral Found of QUST
(No. 0022541).
References
[1] Sagara Y, Kato T. Mechanically induced luminescence changes in molecular
assemblies. Nat Chem 2009;1:605e10.
[
[
[
2] Weder Christoph. Mechanoresponsive materials [Editorial] J Mater Chem
4
. Conclusions
2011;21:8235e6.
3] Chi Z, Zhang X, Xu B, Zhou X, Ma C, Zhang Y, et al. Recent advances in organic
mechanofluorochromic materials. Chem Soc Rev 2012;41:3878e96.
4] Luo J, Li L, Song Y, Pei J. A piezochromic luminescent complex: mechanical
force induced patterning with a high contrast ratio. Chem Eur J 2011;17:
10515e9.
We have synthesized a series of 9,10-bis(N-alkylphenothiazin-3-
yl-vinyl-2)-anthracenes (PT-Cn) with different length of N-alkyl
chains and investigated the optical properties. These aggregation-

34
M. Zheng et al. / Dyes and Pigments 102 (2014) 29e34
[
5] Crenshaw B, Burnworth M, Khariwala D, Hiltner A, Mather P, Simha R, et al.
[21] Yoon S, Park S. Polymorphic and mechanochromic luminescence modulation
in the highly emissive dicyanodistyrylbenzene crystal: secondary bonding
interaction in molecular stacking assembly. J Mater Chem 2011;21:8338e46.
[22] Kei M, Hideyuki N. Mechanofluorochromism of 4-[bis(9,9-dimethylfluoren-2-
yl)amino]benzaldehyde. Dyes Pigment 2013;96:76e80.
Deformation-induced color changes in mechanochromic polyethylene blends.
Macromolecules 2007;40:2400e8.
[
[
[
[
6] Zhang X, Chi Z, Zhang Y, Liu S, Xu J. Recent advances in mechanochromic
luminescent metal complexes. J Mater Chem C 2013;1:3376e90.
7] Taniguchi Y. Organic solid-state laser. J Photopolym Sci Technol 2002;15:
g
[23] Yang Z, Chi Z, Xu B, Li H, Zhang X, Li X, et al. High-T carbazole derivatives as a
183e4.
new class of aggregation-induced emission enhancement materials. J Mater
Chem 2010;20:7352e9.
8] Barbarella G, Melucci M, Sotgiu G. The versatile thiophene: an overview of
recent research on thiophene-based materials. Adv Mater 2005;17:1581e93.
9] Zhao N, Yang Z, Lam J, Sung H, Xie N, Chen S, et al. Benzothiazolium-func-
tionalized tetraphenylethene: an AIE luminogen with tunable solid-state
emission. Chem Commun 2012;48:8637e9.
[24] Wang Y, Liu W, Bu L, Li J, Zheng M, Zhang D, et al. Reversible piezochromic
luminescence of 9,10-bis[(N-alkylcarbazol-3-yl)vinyl]anthracenes and the
dependence on N-alkyl chain length. J Mater Chem C 2013;1:856e62.
[25] Bu L, Li Y, Wang J, Sun M, Zheng M, Liu W, et al. Synthesis and piezochromic
luminescence of aggregation-enhanced emission 9,10-bis(N-alkylcarbazol-2-
yl-vinyl-2)anthracenes. Dyes Pigment 2013;99:833e8.
[26] Liu W, Wang Y, Sun M, Zhang D, Zheng M, Yang W. Alkoxy-position effects on
piezofluorochromism and aggregation-induced emission of 9,10-
bis(alkoxystyryl)anthracenes. Chem Comm 2013;49:6042e4.
[27] Li J, Liu T, Zheng M, Sun M, Zhang D, Zhang H, et al. Dibutylaminophenyl- and/
or pyridinyl-capped 2,6,9,10-tetravinylanthracene cruciforms: synthesis and
aggregation-enhanced one- and two-photon excited fluorescence. J Phys
Chem C 2013;117:8404e10.
[28] Bu L, Sun M, Zhang D, Liu W, Wang Y, Zheng M, et al. Solid-state fluorescence
properties and reversible piezochromic luminescence of aggregation-induced
emission-active 9,10-bis[(9,9-dialkylfluorene-2-yl)vinyl]anthracenes. J Mater
Chem C 2013;1:2028e35.
[
10] Zhao N, Li M, Yan Y, Lam J, Zhang Y, Zhao Y, et al. A tetraphenylethene-
substituted pyridinium salt with multiple functionalities: synthesis, stimuli-
responsive emission, optical waveguide and specific mitochondrion imag-
ing. J Mater Chem C 2013;1:4640e6.
11] Zhang Y, Zhuang G, Ouyang M, Hu B, Song Q, Sun J, et al. Mechanochromic and
thermochromic fluorescent properties of cyanostilbene derivatives. Dyes
Pigment 2013;98:486e92.
12] Liang J, Hu F, Lv X, Chen Z, Chen Z, Yin J. Synthesis, characterization and
mechanochromic behavior of binuclear gold(I) complexes with various dii-
socyano bridges. Dyes Pigment 2012;95:485e90.
13] Sagara Y, Mutai T, Yoshikawa I, Araki K. Material design for piezochromic
luminescence: hydrogen-bond-directed assemblies of a pyrene derivative.
J Am Chem Soc 2007;129:1520e1.
[
[
[
[
[
[
[
[
[
[
14] Sagara Y, Yamane S, Mutai T, Araki K, Kato T. A stimuli-responsive, photo-
luminescent, anthracene-based liquid crystal: emission color determined by
thermal and mechanical processes. Adv Funct Mater 2009;19:1869e75.
15] Zhang Z, Yao D, Zhou T, Zhang H, Wang Y. Reversible piezo- and photo-
chromic behaviors accompanied by emission color switching of two
anthracene-containing organic molecules. Chem Commun 2011;47:7782e4.
16] Li H, Chi Z, Xu B, Zhang X, Li X, Liu S, et al. Aggregation-induced emission
enhancement compounds containing triphenylamineeanthrylenevinylene
and tetraphenylethene moieties. J Mater Chem 2011;21:3760e7.
17] Dong Y, Xu B, Zhang J, Tan X, Wang L, Chen J, et al. Piezochromic luminescence
based on the molecular aggregation of 9,10-bis((E)-2-(pyrid-2-yl)vinyl)
anthracene. Angew Chem Int Ed 2012;51:10782e5.
18] Zhao Z, Liu J, Lam J, Chan C, Qiu H, Tang B. Luminescent aggregates of a
starburst silole-triphenylamine adduct for sensitive explosive detection. Dyes
Pigment 2011;91:258e63.
19] Zhang X, Chi Z, Xu B, Li H, Yang Z, Li X, et al. Synthesis of blue light emitting
bis(triphenylethylene) derivatives: a case of aggregation-induced emission
enhancement. Dyes Pigment 2011;89:56e62.
[29] Liu W, Wang Y, Bu L, Li J, Sun M, Zhang D, et al. Chain length-dependent
piezofluorochromic behavior of 9,10-bis(p-alkoxystyryl)anthracenes. J Lumin
2013;143:50e5.
[30] Schwaebel T, Trapp O, Bunz U. Digital photography for the analysis of fluo-
rescence responses. Chem Sci 2013;4:273e81.
[31] Kim S, Zheng Q, He G, Bharali D, Pudavar H, Baev A, et al. Aggregation-
enhanced fluorescence and two-photon absorption in nanoaggregates of a
0
00
9,10-bis[4 -(4 -aminostyryl)styryl]anthracene derivative. Adv Funct Mater
2006;16:2317e23.
[32] He J, Xu B, Chen F, Xia H, Li K, Ye L, et al. Aggregation-induced emission in the
crystals of 9,10-distyrylanthracene derivatives: the essential role of restricted
intramolecular torsion. J Phys Chem C 2009;113:9892e9.
[33] Zhang X, Chi Z, Zhang J, Li H, Xu B, Li X, et al. Piezofluorochromic properties
and mechanism of an aggregation-induced emission enhancement compound
containing N-hexylphenothiazine and anthracene moieties. J Phys Chem B
2011;115(23):7606e11.
[34] Zhang H, Guo E, Zhang Y, Ren P, Yang W. Donoreacceptor-substituted
anthracene-centered cruciforms: synthesis, enhanced two-photon absorp-
tions, and spatially separated frontier molecular orbitals. Chem Mater
2009;21:5125e35.
20] Wang Q, Liu H, Lu H, Xu Z, Lai G, Li Z, et al. Synthesis, characterization and
solid-state emission properties of arylsilyl-substituted pyrene derivatives.
Dyes Pigment 2013;99:771e8.
[35] Lee S, Cho M, Yoon H, Lee S, Kim J, Zhang Q, et al. Macromol Res 2004;12:484e9.